Your provider will tell you if you need to stop taking any medicines before you have this test. This may include drugs that prevent blood clots (blood thinners).

DO NOT stop or change your medicines without talking to your provider first.

How the Test will Feel

When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or slight bruising. This soon goes away.

Why the Test is Performed

You may need this test if you have an unexplained blood clot, or a family history of blood clots. Protein S helps control blood clotting. A lack of this protein or problem with the function of this protein may cause blood clots to form in veins.

Sometimes, this test is done to find the cause of repeated miscarriages.

Normal Results

Normal values are 60% to 150% inhibition.

Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or may test different samples. Talk to your provider about the meaning of your specific test results.

What Abnormal Results Mean

A lack (deficiency) of protein S can lead to excess clotting. These clots tend to form in veins, not arteries.

A protein S deficiency may be inherited. It can also develop due to pregnancy or certain diseases, including: